The proposed research concerns a molecular description of the steps in the animal cell cycle. Attempts will be made to isolate DNA replicase from S phase nuclei and ascertain the number of subunits, their functions, and time of synthesis in the cell relative to the G1 yields S conversion. The intermediate in DNA replication will be isolated in an attempt to describe the role of RNA synthesis, DNA ligation, and DNA modification in the replication process. The synthesis and turnover of cell membrane proteins will be assessed in an attempt to correlate changes with the G1 yields S-phase conversion step of the cell cycle. Attempts will be made to release cell membrane proteins by mild salt, osmotic, and light detergent treatments and to study the regeneration of these components by the cell. Synchronized cultures of HeLa, bovine lymphocytes, and BHK cells will be used in these studies. Biochemical isolation techniques will involve gel electrophoresis, column chromatography, and sedimentation in velocity and density gradients.